geochemistry, mineralogy and petrography of al-hisa

Journal of Environment and Earth Science www.iiste.org

ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)

Vol.6, No.2, 2016

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Geochemistry, Mineralogy and Petrography of Al-Hisa Phosphate

Rocks and Its Upgraded Ores

Ibrahim A. Mahdi M. Rabba'

Ministry of Energy and Mineral Resources, Geology Directorate/Jordan

Abstract

Several samples from phosphate rock and upgraded ores collected from Al-Hisa mine central Jordan were

investigated geochemically and mineralogical. Mineralogical study showed that the main mineral phases are

Françoise, beside calcite, gypsum clay and silica. The petrography of francolite shows that it is presented mainly

in the form of pellets, ooliths and bioclsts, the matrix formed mainly from calcite, micro-quartz and anhydrite. The

upgrading process causes enrichment of Françoise, clay and gypsum to some extent, and depletion of calcite and

quartz. Thus the TCP increased from 52% in the original phosphate rocks and reaches 64% in the upgraded ores.

The dramatic drop of chlorine in upgrading ores reflects its solubility if the effluent water, that might cause increase

of Cl in surface water bodies.

Keywords: Phosphate, Upper Cretaceous, Upgraded ores, Francolite, TCP, Jordan

1. Introduction

Jordan has huge reserves of phosphate deposits, the main deposits existed in the southern region of the country

(Bender, 1974; Khaled and Abed 1980). The mining industry of phosphate ores consumes up to 6 million m3/year

produced from Al-Abyad and El-Hisa mines alone (Jiries et al. 2004). Sadaqa et al. (2001) have studied the

depositional environment of the phosphate ore all over Jordan using the 14C and 18O isotopes, indicates the

autogenic origin for all the phosphates of Jordan, and evidence for active upwelling. In general the concentrations

of trace elements such as U, V, Cd, Cr, and As are increasing from south to north, for example, U ranged from 40–

60 to 70–80 mg/kg)1 for samples from Esh-Shidyia and Al-Hisa mines, respectively (Jordanian Phosphate Mines

Company (JPMC) 1998; Khaled et al. 1990). At Al-Hisa mine U is found in one layer with an average of 100

mg/kg) (Beerbaum 1977). Abed (1982) found that the U concentration increases towards the north as the sediments

become more marine facies. Ghosheh and Dodeen (1993) showed that other heavy metals and toxic elements in

the Jordanian phosphate rocks are lower compared with several phosphate deposits from the world. Moreover,

similar conclusion was reached by Al-Haiti et al. (2001). Jiries et al. (2004) studied the hydro-chemical and

isotopic characteristics of the effluent water of both mines. They also reported that quality of the effluent water

from Al-Hisa mine was better than that of the Al-Abyad mine, as it shows much lower electrical conductivity (EC)

values, which they attributed to the slight difference in ore geochemical properties. Abed et al. 2008; found that

potential toxic metals behaves as P and are enriched by a factor of more than 1.5 in the diammonium phosphate

(DAP) compared with the input phosphorite. And that the trace metal content in the phosphogypsum is very low.

U sticks to the mineral Françoise during upgrading of the ores, and behaves similar to Ca and P2O5 (Abed 2011).

The phosphate industry is one of the most contaminating sources to the environment, which contributes to

soil, water and air pollution (Vandenhove 2002; Jiries et al. 2004).Hamaiedah and El-Hasan (2011), has found

phosphate mines at Al-Hisa is heavily affecting the particulate matter in the areas around the mines. Al-Hwiti et

al. 2016; investigated the potential environmental associated with the effluent mine waste water from the Eshidiya

mine, the values of conductivity (EC) and sodium adsorption ratio (SAR) indicates that most of the samples are

categorized as C4S1–C4S2. And this water falls into the FAO “slight to moderate restriction on use” category for

irrigation.

The objective of this study is to clarify the geochemical, mineralogical and petrographic characteristics of

Al-Hisa phosphate ores, and to further investigate the characteristics of the phophogypsum generated from these

ores at phosphoric acid plant at Aqaba.

2- Sampling and Analytical methodology

Several hand specimen sized rock samples were collected from Al Hisa Mine in the central part of Jordan as shown

in Figure1. The number of samples is 3 and they were labeled as Hisa-1, Hisa-2 and Hisa-3. Two other samples

collected from the upgraded phosphate raw material, these samples labeled as Ph-1 and Ph-2, which were collected

from the phosphate raw material that used by JPMC-IND COMPLEX in Aqaba.The mineralogical, petrography

and chemical studies were performed to all of them.

Several chemical analyses were carried out on the collected samples, these including X- Ray Fluorescence

(XRF) (PHILIPS 2400) with an attached 72-position sample changer. Pellets were made by fusing 0.8 g of sample

powder and 7.2 g of L2B4O7 in Au/Pt crucible using a flexor machine (Leco 2000) for 3-4 minutes at 1200ºC.

Which used for analyzing the major oxides and trace elements that present in the phosphate samples. Calcimeter

has been employed to identify the calcite content in the investigated phosphate ore samples;in addition to that the



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loss of ignition has been examined for the three mentioned samples at 900 ºC. Moreover, Fisher assay was utilized

to identify the organic carbon content. And X-Ray Diffraction (X-Ray Diffraction system (Siemens D5000 powder

diffractometer with Cu-Kα-radiation source) equipped with a secondary graphite monochromator (40-position

sample stage). The samples were scanned between 10º and 70º 2θ, using Ni-filtered Cu-Kα-radiation (40 kV, 40

mA), divergent and scattering slits of 0.02 mm, a receiving slit of 0.15 mm with stepping of 0.01 mm and scanning

speed of 3º/min. The XRD analysis was carried out at the Institute of Geosciences, University of Erlangen-

Nuremberg, UK. This machine was employed to identify the major and trace mineral components of some

collected phosphate ore samples. Three thin sections were prepared from the Al-Hisasample for microscopic

examination. Nikon polarized microscope with a digital microscopic camera have been employed for the

petrography and mineralogical studies.

Fig. 2. Map showing the location of AL-Hisa mine

3. Results & Discussion:

3.1 Geochemical characteristics of Al-Hisa phosphate rocks and upgraded ores

Several representative samples collected from the phosphate raw materials that used in Industry Complex for

producing phosphoric acid, these samples were numbered as Ph-1, Ph-2. In addition to a rock phosphate ore sample

has been collected from Al Hisa Mine namely Hisa-1, Hisa-2 and Hisa-3. All these samples were analyzed by XRF

to estimate their chemical composition, and the results are shown in Tables 1&2.

The results obtained from the XRF for the upgraded powdered samples show no significant differences in

the major chemical components relating to the small variation in the apatite, calcite and quartz minerals content of

the powdered samples. The P2O5 content of these samples, as seen from the XRF analysis, ranges between 28.5 to

30.16%, averaging 29.33%. The CaO content ranges between 48.10 to 49.13 %, averaging 48.62. The CO2 results

obtained show that there is a considerable quantity of calcite and Françoise minerals in the analyzed phosphate ore

samples, CO2 was 6.52 in both samples. Fluoride element was detected in a considerable amount which gave an

indication on the presence of apatite mineral in the analyzed ore samples, because both of them are usually

associated with each other in the nature. According to the XRF analysis that carried out on the Jordanian Phosphate

(upgraded samples) for F element, the results obtained show that it ranges between 3.90 to 4.00%, averaging 3.95%.

Other detected oxide elements are Al2O3, SO3, SiO2 and MgO; these oxides are present due to the presence of

cryptocrystalline quartz (chalcedony), gypsum and clay minerals in phosphate rock sample.

The analysis of the hard phosphate rock sample which is not upgraded show that P2O5 and CaO lower in

consents than the previous upgraded samples, while SiO2 and Cl contents are much higher as seen in Table 1.



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Table 1: Results obtained from XRF for major oxides in the phosphate ore samples and upgraded ore

samples.

Oxides Sample Identification

Ph-1 Ph-2 Hisa-1 Hisa-2 Hisa-3

P2O5 30.16 28.5 24.0 23.8 24.2

CaO 49.13 48.1 44.2 44.02 44.1

SiO2 7.61 9.00 16.6 15.7 17.7

MgO 0.35 0.366 0.21 0.20 0.31

Al2O3 0.527 0.823 0.32 0.33 0.30

Fe2O3 0.255 0.385 0.37 0.32 0.41

Na2O 0.6 0.575 0.8 0.76 0.88

K2O 0.031 0.00 0.05 0.05 0.06

SO3 1.23 1.28 0.83 0.86 0.82

TiO2 0.008 0.03 0.013 0.014 0.017

MnO 0.015 0.0105 0.008 0.006 0.009

CO2 6.52 6.52 9.58 9.44 9.67

F % 3.90 4.00 2.58 2.62 2.49

L.O.I 8.15 9.47 9.50 9.61 9.47

Table 2: XRF results for trace elements concentrations in phosphate ore samples and upgraded

samples.(ppm)

3.2 Mineralogy and petrography of Al-Hisa phosphate rocks and upgraded ores

3.2.1 Mineralogical results

The mineral identification was carried out on the collected samples.The main methods for identification the

mineral components of the phosphate ore samples is the XRF method to calculate the percentage of minerals in

the phosphate ore samples. Calcimeter was employed to determine the amount of calcite content in the ore samples

and powder X-Ray diffraction used to identify the major and trace minerals component of the phosphate ore and

upgraded samples.

Sedimentary Jordanian phosphates are mostly composed of varieties of apatite Ca5 (PO4)3(OH, Cl, F),

mainly in the form of Françoise pellets (carbonate-fluorapatite) Ca5(PO4.CO3)3F with molecular weight equal to

486.82gm. Dahllite apatite mineral (carbonate hydroxylapatite) was found in lesser extent. This was evidenced by

the X.R.D results of the analyzed phosphate ore samples revealed that the main apatite mineral is fluorapatite type

as revealed in Figure 2.

Trace Elements

Sample Identification Standard

Error Ph-1 Ph-2 Hisa-1 Hisa-2 Hisa-3

Cl 718 1123 4893 4670 4915 0.0059

Zn 159 199 101 109 89 0.0031

Cr 118 96 9.0 9 8 0.0023

V 75 51 79 73 80 0.0015

U 62 62 81 65 88 0.0007

Y 50 68 49 47 54 0.0005

Zr 28 55 48 44 43 0.0006

Ni 22 11 7 7 9 0.0004

Cu 17 26 24 28 25 0.0004

Sr 1160 1314 1036 995 1110 0.0190



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Fig. 2 : XRD chart showing the main mineral phases in the upgraded phosphate ore sample number Ph-1.

The calculation of Françoise mineral percentage in the analyzed phosphate ore samples was depending on

P2O5, CaO, CO2, and F concentrations. Those figures were compared with the standard amounts of P2O5, CO2 and

CaO in the Françoise mineral which illustrated in Table 3.

Table 3: Showing chemical composition of the standard francolite mineral.

Elements % Oxide %

Ca 41.16 CaO 57.60

P 15.91 P2O5 36.45

C 1.23 CO2 4.52

O 37.79 O 0.00

F 3.90 F 3.90

Total 100%

The apatite calculations revealed that the most abundant mineral in the phosphate ore samples was francolite.

The estimated amounts of mineral in the upgraded samples was 80.45%, while the francolite mineral (apatite)

content in the ore rock sample was 65.84% . The color of the mineral is yellowish white.

The calculation percentages of the montmorillonite clay mineral (CaO.2 (Al, Mg) 2SiO4. 10 (OH) 2! 4H2O)

as recognized by X.R.D were depending mainly on Al2O3 content in the analyzed ore samples, the standard

montmorillonite mineral consist of 51% SiO2, 20% Al2O3, 3% MgO, 1.5% CaO, 8% H2O+ (combined water) and

15% H2O-, the color of the mineral is yellowish white to light green. By comparing the Al2O3 in the phosphate

ores with the Al2O3 that present in the standard montmorillonite mineral, it can be said that the mineral forms about

3.44% in upgraded sample and 1.6% in rock sample. The loss in clay mineral were found to be removed in effluent

and slime during ore upgrading (El-Hasan, 2006).

Gypsum mineral contents are not accurate in the phosphate ore samples due to the presence of organic

matter in the analyzed samples which contains also sulphur in its contents. This doesn't mean that the gypsum is

not present in the samples, as the petrography studies that carried out later on the ore samples approved that gypsum

mineral is present. It can be conclude that the exactly amounts of gypsum in the samples depending on the SO3

contents is not accurate due the presence of the SO3 in both organic and inorganic forms. The estimated amounts

of gypsum were 2.22% for the upgraded ore sample, meanwhile it is 1.78% in rock sample.

The calculated amounts of chalcedony (cryptocrystalline quartz) in the ore samples were 6.60% in the

upgraded ore samples and 15.78% in rock samples respectively. These calculations were depending on the SiO2

contents of the analyzed samples. The amounts of SiO2 being divided between chalcedony and montmorillonite

minerals, because the later mineral contains about 50% SiO2, while the chalcedony contains 100% SiO2. The

Calcimeter instrument was employed for estimation the CO2 content in the carbonate minerals for the upgraded

ore and rock samples. The results obtained show that the calcite content were 6.56% and 15.01% respectivelyThe

results obtained from the calculations of mineral contents of the analyzed phosphate ore samples are listed in Table

4.



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Table 4: Showing the Calculated minerals that depending on the XRF analysis that obtained in Table 1.

Mineral % Upgraded ore sample Rock sample

Francolite 80.45 65.84

Calcite 6.56 15.01

Gypsum 2.22 1.78

Clay 3.44 1.60

Cryptocrystalline quartz 6.30 15.78

Depending on the obtained concentration of P2O5, the Tri-calcium Phosphate TCP was calculated using the

equation TCP = P2O5* 2.185 (Momani, 2011), then values of TCP are listed in Table 5.

Table 5: Showing the Calculated Tri-Calcium Phosphate (TCP) depending on the XRF analysis that obtained from

XRF

Sample Identification Tri-calcium phosphate (TCP)

Ca3(P2O4)2

Upgraded ore sample 64.14

Rock sample 52.44

3.2.2 Petrography results

The main components of phosphate rock as seen in thin sections are:

1.Phosphate pellets: They are composed of collophane (cryptocrystalline apatite) with grain size ranges between

0.5 to 5.2 mm; vary in shape from spherical to ovoidal and very well-sorted. Under the plane polarized light (PPL),

their color ranges from light brown, yellowish brown to black. The black colors may be due to presence of organic

matter inclusions and indicative of formation under reducing conditions Figure3.

Fig 3 Anisotropic phosphate collophane (rounded pellets), ppl. Mag. 4x

2. Under crossed polarized light (XPL) the phosphate pellets are isotropic and showing a very weak birefringence

(dark colors) so, it was too difficult to see any internal structures that may be present in the grains of phosphate

Figure 4.

Fig 4 Isotropic phosphate collophane (rounded pellets), xpl. Mag. 4x



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3.Phosphate ooliths: These grains show a well-defined concentric structure with some times a nuclei occurred in

the centers of the phosphate grains. They are usually consisting of collophane alternating with Françoise laminate

Figure 5.

Fig 5 Anisotropic rounded pellets with concentric texture, ppl. Mag. 4x

3. Phosphate nodules (intraclasts): They are large grains formed in the sea-floor, circular to elliptical shape. They

are described as a coated bioclasts, comprises of nucleus (bioclasts) surrounded by a coating of micrite which

makes a sharp contact with the internal materials. The coating is not laminated.

4. Bioclasts (skeletal particles): They are the remains, complete or fragmented of hard parts of carbonate or apatite-

secreting organism. Anisotropic phosphate (apatite), occur as teeth and bone fragments, forms about 20%. Some

of bone fragments have shown an internal structure filled with a fine phosphate material Figure 6.

Fig 6 Isotropic collophane pellets with teeth fragments, xpl. Mag. 4x

1. Cement Materials: The main cement materialthat surrounding the phosphate components was spray

calcite forms more than 20% in some views Figure 7.



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Fig 7 Calcite cementing material surrounding dark collophane pellets, xpl. Mag 4x

The other cement material present in the phosphate rock is anhydrite but occur as a minor content (< 3.0%).

1. Matrix Material: Many of the phosphate grains are set in a matrix of micro-quartz (chert) forms more

than 20% in some views Fig 8. The grain packing clearly indicates that the chert represents an original

matrix.

Fig 8 Cryptocrystalline silica matrix surrounding the dark collophane pellets. Xpl. Mag. 4x

The textures of phosphate rock is the grain-stone texture according to Dunham classification (1962). Where the

rock is grain-supported with a spar calcite cement and cryptocrystalline quartz matrix.

Conclusions

The Jordanian phosphate ore deposits at Al-Hisa area that belongs to the Upper Cretaceous rocks, were mined

commercially since 70’s of the last century. The studies indicated ore reserves of 2000 million tones with an

average P2O5 content of 30%. In the upgraded ore large quantities of Calcite, Clay and Silica were removed through

washing with fresh water. The results upgraded ore have Françoise increased from 65.84 up to 80.45%, Tri-

Calcium Phosphate (TCP) Ca3 (P2O4)2 is also increased from 52.44 up to 64.14. Beside that few trace elements

such as Zn and Cr get enriched in the upgraded ores, while Cl is very high in the original rocks.

The mineralogy and petrography studies revealed that the most abundant mineral in the upgraded

phosphate ore samples was Françoise, that found in many forms as pellets, ooliths and bioslasts, the cementing

materials are spray calcite, micro-quartz and the anhydrite.

Acknowledgment

The author is very thankful to the Head of laboratory department at the Natural Resources Authority for his great

help in the analytical procedures of this work.



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geochemistry, mineralogy and petrography of al-hisa

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